Id even go as far to say Yellow Nutsedge. go to your local chemical shop and if you got a License, the'll let you buy something called MANAGE its a small container about as large as a big bottle of tylenol. it is specifically for Nutsedge.....works good, and will not harm most grasses. It has a side effect in that it also gets out dollar weed, but is not labeled as such

Sedge is a water freindly plant, but once established and can survive well on low water...